The implementation of a comprehensive therapeutic interchange program is described. The need to reduce the number of telephone calls to physicians about nonformulary drug orders, reduce drug costs, and maximize the effectiveness of drug therapy prompted the development of an automatic therapeutic interchange program at a 273-bed nonteaching community hospital. Pharmacists and physicians agreed that a telephone call to discuss every nonformulary drug order was unnecessary. The pharmacy department presented the automatic interchange program to the pharmacy and therapeutics committee. The program was reviewed by the committee, the hospital attorney, and medical staff members and was instituted in 1986 for drug products, such as vitamins and antacids, for which interchanges are noncontroversial. A newsletter describing the program was distributed, and inservice education sessions were held. A reminder was placed on order forms that an interchange for nonformulary drugs would be made unless the nonformulary agent was deemed "medically necessary" by the physician. In such cases, the physician is contacted to discuss the therapeutic alternative. As acceptance of the program and cost efficiencies were demonstrated, more controversial agents were phased in during subsequent years. It was difficult to obtain approval to add some agents, such as third-generation cephalosporins, to the program, but noncompliance and confusion have been minimal. An automatic therapeutic interchange program has worked well at this institution since 1986.